A thermal processing chamber, as used herein, refers to a device that uses light energy to heat objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding a semiconductor wafer and a light source that emits light energy for heating the wafer. For monitoring the temperature of the semiconductor wafer during heat treatment, thermal processing chambers also typically include radiation sensing devices, such as pyrometers, that sense the radiation being emitted by the semiconductor wafer at a selected wavelength. By sensing the thermal radiation being emitted by the wafer, the temperature of the wafer can be calculated with reasonable accuracy.
One type of thermal processing chamber operates at or near atmospheric pressure. These types of processing chambers typically include a gas inlet and a gas outlet for continuously circulating a gas through the chamber during processing of semiconductor wafers. The gas that is circulated through the chamber can be, for instance, an inert gas for preventing the semiconductor wafer from undergoing any adverse chemical reactions during the heating process. Alternatively, the gas circulated through the chamber can contain a gaseous reactant which reacts with the surface of a semiconductor wafer to form a film or coating on the wafer in fabricating a semiconductor device.
In the past, problems have been experienced in the operation of the above-described atmospheric thermal processing chambers due to gas leaks present in the chamber walls. For instance, it is not uncommon for leaks to develop around the movable doors that are used to insert and remove the semiconductor wafers and around various fittings and spectral windows that may be present on the chamber. It has been found to be expensive and impractical to locate the leaks and/or to leak test the chamber itself. For instance, in order to leak test a chamber, the chamber must be taken off line and the process being conducted in the chamber must be stopped.
Many adverse consequences can result should a substantial amount of gases leak into or out of the thermal processing chamber during operation. For instance, one major concern is the infiltration of oxygen from the outside environment into the chamber during some applications. In particular, oxygen can adversely react with a gas being fed to the chamber, can react with the semiconductor wafer, or can otherwise adversely interfere with the process. Besides oxygen, it is also important that substantial amounts of moisture do not leak into the thermal processing chamber either.
In other applications, it is important that none of the gases being fed to the chamber are permitted to escape from the chamber into the outside atmosphere. For instance, during some applications, the gases that are used to react with the semiconductor wafer are hazardous to the environment or are toxic.
Problems experienced with gases either leaking into or out of atmospheric thermal processing chambers have been further magnified in the past due to the exhaust systems that have been connected to the chambers. For instance, atmospheric thermal processing chambers, when installed at a particular facility, are typically connected at the gas outlet to a preexisting exhaust system present at the facility. Such exhaust systems, which can vary from site to site, are usually connected to various different equipment and machinery. Thus, the exhaust systems can undergo large fluctuations in pressure depending upon the particular circumstances. Such fluctuations can have a direct impact on the pressure within the thermal processing chamber and the rate at which gases flow through the chamber. The pressure in a thermal processing chamber and the exhaust rate have a direct impact, in turn, on the amount of gases that may leak into or out of the chamber.
In the past, atmospheric thermal processing chambers typically did not contain any controls that normalized the exhaust rate of the gases out of the chamber or compensated for the exhaust system that was connected to the chamber. Further, little was done to prevent gas leakage into or out of the chamber.
Thus, a need exists for a method that minimizes the amount of gases that leak into an atmospheric thermal processing chamber. Similarly, a need also exists for a method that prevents process gases from leaking out of the chamber during operation. Such controls are especially necessary due to the increasing demands that are being placed upon the preciseness at which semiconductor wafers are heat treated and at which semiconductor devices are fabricated. Consequently, there is currently a need to develop more precise control over the process parameters of thermal processing chambers in order to better control the heat treating process and the deposition of films on semiconductor wafers.